feat: update to kotlin 1.9.21

[DarkAtra]

Now requires at least Java 21 -> new major release

This PR tries to update to the latest kotlin version as described here: oracle/graal#6957 (comment)

[DarkAtra]

Tests are still failing in native-image. I'll have to double check that the paketo builder is using the correct graalvm version during builds.

[DarkAtra]

Tests are now passing but the project currently requires at least java 21 to run. This is likely not a huge issue but would force us to release this as a new major version although the change is only necessary for GraalVM (see oracle/graal#6957 (comment)). I'll investigate the following solutions:

• use GraalVM 21 to produce java 17 bytecode - preferred
• only use GraalVM 21 when building the native image and use JDK 17 for JVM builds

[sonarqubecloud]

Quality Gate passed

Kudos, no new issues were introduced!

0 New issues
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud

[DarkAtra]

Building the native image locally using ./mvnw clean spring-boot:build-image -Pnative currently fails. Tests are passing though... This might be related to building on Arm64. I'll attempt to create a pre-release on Github later. If this still fails, it probably has something to do with passing --strict-image-heap to GraalVM.

[DarkAtra]

Building the native image locally using ./mvnw clean spring-boot:build-image -Pnative currently fails. Tests are passing though... This might be related to building on Arm64. I'll attempt to create a pre-release on Github later. If this still fails, it probably has something to do with passing --strict-image-heap to GraalVM.

The build failed because i removed the native-maven-plugin a few commits ago. Re-adding it, explicitly managing the GraalVM version via BP_JVM_VERSION and dropping the --strict-image-heap argument fixed the issue.

One quirk remains: the actual (native) build environment differs from the (native) test environment. Tests require --strict-image-heap and are using OpenJDK Runtime Environment GraalVM CE 21.0.2+13.1 (build 21.0.2+13-jvmci-23.1-b30) (as of right now). The docker build uses Java version: 21.0.2+14-LTS, vendor version: Liberica-NIK-23.1.2-1 without --strict-image-heap. This could lead to us publishing a broken native image if something is wrong with the build environment but tests are passing. This is already the case on main though, so i'll ignore this issue for now.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud